1. Field of the Invention
The present invention relates to an ink jet recording apparatus which records by causing ink to adhere to a recording medium and, in particular, to an ink jet recording apparatus equipped with a mechanism which makes possible satisfactory recording by a recording means.
2. Description of the Related Art
A recording apparatus having the function of a printer, copying machine, facsimile apparatus or the like, or a recording apparatus used as the output device of a composite apparatus or a work station including a computer, word processor or the like, records images on a recording medium, such as paper or a thin plastic sheet (OHP or the like), in accordance with image information. There are various types of such recording apparatuses, which are classified according to the type of recording means they use, such as: an ink jet type, a wire dot type, a thermo-sensitive type, a thermal transfer type, a laser beam type, etc.
In a serial-type recording apparatus, in which a main scanning is performed perpendicular to the direction in which the recording medium is fed, image recording is effected on the recording medium, which has been set at a fixed recording position, by a recording means mounted on a carriage which moves along the recording medium. After recording one line of information, the recording medium is fed by a fixed amount (pitch feed). After that, the recording (i.e., the main scanning) of the next line is effected. By repeating this operation, image recording is performed over the entire recording medium. In a line-type recording apparatus, which records solely by sub-scanning, that is, feeding the recording medium in the feed direction, the recording medium is first set at a fixed recording position to record one line of information collectively, and then is fed by a fixed amount (pitch feed). Subsequently, the next line is recorded collectively. By repeating this operation, image recording is effected over the entire recording medium.
Both the serial and line-type recording apparatuses may use an ink-jet type recording system, in which recording is effected by ejecting ink from recording means (a recording head) onto the recording medium. This recording system has various advantages. For example, (a) the recording means can be made compact; (b) an image of a high level of resolution can be recorded at high speed; (c) the operating cost is relatively low since ordinary paper which has undergone no special processing can be used; (d) because it is a non-impact system, the noise level is relatively low; and (e) a color image can be easily recorded by using inks of various colors. Above all, this recording system is especially advantageous when used in a line-type recording apparatus, in which a large number of ejection nozzles are arranged in the paper-width dimension, since it allows recording at still higher speeds.
In particular, ink-jet type recording means (recording head), in which ink is ejected by utilizing heat energy, can be easily produced as a small-sized recording head having liquid passages (ejection nozzles) arranged at high density, by forming electro-thermal conversion members, electrodes, liquid passage walls, top plate, etc. on a substrate by semiconductor fabrication processes, such as etching, evaporation or sputtering.
The ink jet recording apparatus, described above, generally employs a recording head on which minute ejection nozzles are arranged, so that if the ink has become unsuitable for ejection or recording as a result of intrusion of bubbles, dust or the like into the interior of the ejection nozzles or an increase in the viscosity of the ink due to evaporation of some of the ink solvent, some portion of the ink near the ejection nozzles is discharged from the nozzles to refresh the ink, thereby eliminating the factor causing defective ejection and restoring the proper ejecting condition.
An ink-jet recording apparatus is equipped with a restoring mechanism for restoring proper ejection. Such a mechanism typically consists of a cap capable of covering the face of the recording head on which the ejection nozzles are formed (hereinafter referred to as the "nozzle surface") and a pump communicating with this cap and exerting a sucking force. There are two types of ejection restoring operations: in one, ink-ejection-energy generating elements inside the ejection nozzles are operated with the cap opposed to the nozzle surface of the head, thereby causing some ink to be discharged; in the other, some ink is forcibly sucked out from the nozzles by exerting a sucking force with the nozzle surface sealed by the cap pressed against it. In some cases, the head is held in a "capped" state when it is not being operated, thereby preventing evaporation of ink through the nozzle surface of the head, or clogging of ink due to thickening or clinging thereof.
In an ink jet recording system, a mechanism for restoring and a mechanism for maintaining a satisfactory ink ejecting condition of the recording head are essential.
U.S. Pat. No. 4,317,124 discloses an example of such a system, according to which the recording head is kept in a capped state when no recording is being performed, with the space defined by the cap and the head being filled with ink so as to keep the head moist, thereby preventing evaporation of ink through the nozzle surface of the recording head, etc. A problem with this mechanism is that the ink filling the above-mentioned space may leak as a result of expansion of the ink due to environmental changes.
Further, it should be noted that in some cases it is impossible to secure a sufficiently high level of reliability if maintenance of the head in a condition where recording is frequently performed (short-term storage) and maintenance thereof when the recording head is not used for a long period of time (long-term storage) are conducted in the same manner.
A means of overcoming this problem is described, for example, in Japanese Patent Laid-Open No. 60-151059, according to which only the capping is effected for a short-term storage. For long-term storage, the ink in the recording head is entirely discharged and the head is cleaned with cleaning liquid before storage. Accordingly, a dedicated storage section, feeding section, etc. for the cleaning liquid are necessary, so that the apparatus must have a very large size.
Further, if the ink in the recording head is entirely drawn out for long-term storage, it is necessary to re-fill the head with ink when recording is to be performed again. Moreover, such re-filling has to be conducted twice so as to flush any remaining cleaning liquid from the head, so that the consumption of ink increases, resulting in high operating costs.
Apart from these arrangements, a structure has been proposed in which a porous body is provided inside the cap. This porous body temporarily traps the discharged ink to provide a moistening effect.
The ink discharged from the recording head is sucked by a pump and collected in a discharged-ink sump. However, as a result of the above-described sucking operation, the porous body in the cap is in a squeezed condition, so that the amount of ink retained by the porous body is small, resulting in an insufficient moistening effect. Thus, in the prior-art relying upon a sucking operation, a sufficient evaporation suppressing effect for the portion of the ink near the ejection nozzles cannot be obtained.
Thus, with the various methods which have been proposed up to the present, it is impossible to effect restoring and maintenance of proper ejection easily and reliably with respect to both long-term and short-term storage.